Though quantum theory is already more than hundred years old, the physics of quantum information is a relatively young field of research. It aims at exploring the physical foundations of information and at developing efficient methods for processing quantum information. The questions driving this research field reflect a profound change in the general attitude towards the fundamental aspects of quantum theory. So far, research on the foundations of quantum theory has mainly been concerned with the theoretical exploration of those particular features which distinguish quantum theory from classical physics. One of the main intentions of this new research area is to exploit these specific features for technological purposes. Thereby characteristic quantum phenomena, such as entanglement, the linear superposition principle and the resulting specific quantum correlations, play an important role. However, these characteristic quantum phenomena are rather fragile. They can be destroyed easily by uncontrollable couplings to an environment. Thus, overcoming the resulting phenomenon of decoherence is a major task which has to be solved in order to achieve significant quantum technological advances.

By now quantum information has become an interdisciplinary subject which attracts not only physicists but also researchers from other communities, most prominently computer scientists and electrical engineers. For a discussion of some basic problems and methods in this research field see for example

G. Alber, T. Beth, M. Horodecki, P. Horodecki, R. Horodecki, M. Rötteler, H. Weinfurter,
R. Werner, A. Zeilinger, Quantum Information: An Introduction to Basic Theoretical Concepts and
Experiments (Springer, Berlin, 2001)

D. Bouwmeester, A. Ekert, A. Zeilinger, The Physics of Quantum Information (Springer, Berlin, 2000)

In our group, we currently investigate e.g. the following topics:

T.Kiss, S. Vymetal, L.D.Toth, A. Gabris, I. Jex, and G. Alber, Phys. Rev. Lett. 107, 100501 (2011)

J. Novotny, G. Alber, and I. Jex, Phys. Rev. Lett. 107, 090501 (2011)

J. Novotny, G. Alber, and I. Jex, New Journal of Physics 13, 053052 (2011)

I. Jex, G. Alber, S. N. Barnett, and A. Delgado, Prog. Phys. 51, 171 (2003)

Though many quantum processes are capable of copying or entangling some pure input states of a quantum system with a known reference state of a second quantum system, it is not easy to achieve this goal for all possible input states. In view of this difficulty, it is of particular interest to investigate universal (or covariant) processes, which are able to entangle or copy all pure input states of a quantum system which are members of a particular set or of a linear space in an optimal way. Thereby, the restrictions imposed on these processes by the linear character of quantum theory are not only of practical interest, but they also hint at fundamental limits of quantum theory itself. Most recently we have investigated the problem of the optimal copying of pure two-qubit states of a given degree of entanglement.

J. Novotný, G. Alber, and I. Jex, Phys. Rev. A 73, 062311 (2006)

J. Novotný, G. Alber, and I. Jex, Phys. Rev. A 71, 042332 (2005)

G. Alber, A. Delgado, and I. Jex, Quantum Information and Computation 1, 33 (2001)

Prof. Dr. Gernot Alber

Institut für Angewandte Physik

Hochschulstraße 4a

64289 Darmstadt, Germany

+49-6151/16-20400 (fax: 20402)

gernot.alber@physik.tu-...